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In either case, the inclusions had to be present before they could be included in the younger rock, therefore, the inclusions represent fragments of an older rock.This principle is often useful for distinguishing between a lava flow and a sill.Principles of Stratigraphy Stratigraphy is the study of strata (sedimentary layers) in the Earth's crust.Geologist in the 1800s worked out 7 basic principles of stratigraphy that allowed them, and now us, to work out the relative ages of rocks.
Thus rocks that we now see inclined or folded have been disturbed since their original deposition.He concluded that process that are currently operating on the Earth must be the same processes that operated in the past.This principle is often stated as "the present is the key to the past".Look at the many photographs of the Grand Canyon in your textbook.
Note that you can follow the layers all along the walls of the canyon, and you can find the same layers on both sides of the canyon.
Principle of Original Continuity If layers are deposited horizontally over the sea floor, then they would be expected to be laterally continuous over some distance.